Abstract

Using a vocoder, median-plane sound localization performance was measured in eight normal-hearing listeners as a function of the number of spectral channels. The channels were contiguous and logarithmically spaced in the range from . Acutely testing vocoded stimuli showed significantly worse localization compared to noises and click trains, both of which were tested after feedback training. However, localization for the vocoded stimuli was better than chance. A second experiment was performed using two different 12-channel spacings for the vocoded stimuli, now including feedback training. One spacing was from experiment 1. The second spacing (called the speech-localization spacing) assigned more channels to the frequency range associated with speech. There was no significant difference in localization between the two spacings. However, even with training, localizing 12-channel vocoded stimuli remained worse than localizing virtual wideband noises by 4.8° in local root-mean-square error and 5.2% in quadrant error rate. Speech understanding for the speech-localization spacing was not significantly different from that for a typical spacing used by cochlear-implant users. These experiments suggest that current cochlear implants have a sufficient number of spectral channels for some vertical-plane sound localization capabilities, albeit worse than normal-hearing listeners, without loss of speech understanding.

Received 25 June 2009Revised 04 December 2009Accepted 09 December 2009Published online 05 February 2010

Acknowledgments:

We would like to thank our listeners for participating in this study and Michael Mihocic for running the experiments. We would also like to thank the Associate Editor John Middlebrooks, Fred Wightman, and an anonymous reviewer for comments about a previous version of this work. Portions of this study were presented at the Conference on Implantable Auditory Prostheses in Lake Tahoe in 2009. This study was funded by the Austrian Science Fund (FWF Project No. P18401-B15).